The general field of labeling in which a label is provided without a backing is generally termed the field of "linerless labels". In linerless label systems, a substrate such as plastic film is repeatedly printed with the label image on one side and coated with an adhesive on the other side. The substrate, usually in roll form, is fed through an applicator which severs and applies the labels directly to the surface of a container such as a milk container, oil container or the like. Various systems can be found in the prior art in which the printed substrate is coated with all adhesive on one side and is provided in roll form which eliminates the need for a backing.
U.S. Pat. No. 5,431,763 discloses a linerless label system which utilizes a transparent paper or plastic film substrate. The substrate is provided in web roll form and is printed on one side with an image which is overcoated with an adhesive. The opposite surface has release characteristics. When applied, the web is fed across the surface of an anvil plate. A die engages the anvil plate and cuts the label from the web, which label is then transferred to the surface of an item such as a plastic container.
The applicator equipment described in the '763 patent includes an unwind shaft on which the roll is mounted. The web is fed across the anvil plate which defines an aperture which receives a reciprocal transfer member. The transfer member has a recess which contains a porous perforated surface or material such as a sponge. The transfer member is operatively connected to a plunger or actuator and the interior of the member communicates with a low vacuum source. An oppositely disposed cooperating clamp plate receives an interchangeable die such as a steel rule or machined die which cooperates with the anvil plate to sever the label when the two are brought into engagement. The web is pre-marked with locator or registration marks which are sensed by an optical reader or other sensor. The applicator unit is positioned adjacent a conveyor line along which the articles to be labeled move. A typical application is the labeling of plastic milk bottles. A microswitch or other sensor senses the presence of an article aligned with the applicator unit. The optical reader or other sensor senses the registration marks and causes the clamping plate to retract bringing the die against the substrate and the anvil plate at the proper location. The die cuts the label from the web and the transfer member extends to transport the severed label which is held in place on the transfer member by a vacuum. The adhesive on the label surface adjacent the article secures the label to the article and the vacuum is then released allowing the transfer member to return to a retracted position so the next printed label on the web may be advanced. If the substrate is transparent, the image is preferably on the surface of the substrate which is applied to the container, protecting it from moisture, chemicals or other damaging environmental elements which may be present. The die being a steel rule or machined die is of simple construction and may easily be changed in accordance with the requirements of the label configuration.
The system described above works well and has been commercially accepted. However, in some instances, it is possible, particularly over prolonged uses, for adhesives to accumulate on the die surface which will impair the operation of the unit by impeding the retraction of the die from the web or impair the transfer of the severed label to the article.